He was drafted by the Sta. Lucia Realtors, but after playing 2 seasons he was dealt to the Coca-Cola Tigers along with the aging Kenneth Duremdes and Ricky Calimag in exchange for Denok Miranda, Manny Ramos and Coca-Cola's 2007 second round draft pick. Cabagnot led all rookies during his rookie year in scoring, assists, steals and minutes played. He was third in the league in the assist-to-turnover ratio behind Jimmy Alapag and Johnny Abarrientos. The 6-0 southpaw is one of the prolific guards in his generation. On January 5, 2010, he was traded to the Burger King Whoppers along with Wesley Gonzales, for Gary David and Chico Lanete. He played for several games with Burger King, finishing at the 8th spot of the 2009-10 PBA Philippine Cup. During the off-season of the 2009-2010 Fiesta Conference, he was traded to the San Miguel Beermen, for Mike Cortez. As a Beermen, Cabagnot quickly emerged as the starting quarterback for the team. Cabagnot dropped game winning shots during eliminations earning his nickname "Crunch Time Cabagnot". He did it on Alaska Aces, B-Meg Derby Ace Llmados scoring a basket on crucial possession. During Game 1 of the 2010 - 2011 PBA Philippine Cup semifinals series against the crowd favorite Ginebra Gin Kings, Alex made a clutch basket leaving the Gin Kings with only over a second. This nailed the series to a 1 - 0 lead in favor of the Beermen. SMB eventually won the duel in six games 4 - 2. In 2011, Cabagnot together with Arwind Santos and Danny Ildefonso lead Petron Blaze Boosters to a Governor's Cup title by hacking out a 4-3 decider in 7 games, thus foiling the Grand Slam bid of Talk N Text & captured his first PBA crown as a player. On February 18, 2014, he was part of a complex four-team, seven player trade which sent him to GlobalPort. With his new team, he reunites with old teammate Jay Washington and provided veteran leadership. He said, " came a little bit as an ‘I-didn’t-see-it-coming,' but when it did sink in, I just have to be a pro, go to the next team and try to do what I did with Petron and my other teams before". On June 11, 2014, Cabagnot almost recorded a triple-double for GlobalPort Batang Piers as he racked up 19 points, 8 rebounds and 10 assists but in a losing effort to the Air21 Express. On October 26, 2014, Cabagnot recorded 21 points, 10 rebounds and 3 assists in a win over the Barako Bull Energy Boosters. During the playoffs of the 2014–15 PBA Philippine Cup, Alex Cabagnot was traded back to San Miguel for Sol Mercado. On October 14, 2016 Cabagnot was recognized during the PBA Leo Awards Night as he was named to the PBA Mythcial Second Team. On June 21, 2019, during the 2019 Commissioner's Cup, Cabagnot scored a conference-high 31 points to go along with 4 rebounds and 6 assists in a win over the Alaska Aces. He led the Beermen in a much-needed win as they now have a record of 2-3 for the conference.
